1. Field of the Invention
The present invention relates an asynchronous transfer mode (ATM) switching device that is a fundamental art for a B-ISDN.
2. Description of the Related Art
In recent years, various information communications permitting low to high transmission rates have been developed. An ATM-related art has been regarded as a key to a success in reducing a load of an exchange that controls information transfer, and in integrating communication modes. In the field of the ATM-related art, an ATM switching device for switching ATM cells quickly and readily is attracting attention.
A conventional ATM switching device, for example, as shown in FIGS. 1a and 1b, requires an ATM switch element for switching an ATM cell, and line handlers for processing information necessary for switching an ATM cell based on header information (including six parameters GFC, VPI, VCI, PT, CLP, and HEC) of an incoming ATM cell, and for feeding the resultant information to the ATM switch element. Namely, when an ATM switch element switches an ATM cell, header information of the ATM cell must be used to switch the ATM cell.
In the above conventional device, however, where control information and address information constituting header information of an ATM cell are used as they are, a problem occurs in that control for switching an ATM cell becomes complicated since an amount of control information is insufficient and only a single address can be set. Also, a drawback arises in that respective loads to each ATM switch element get larger.
From the above, the performance of an entire ATM switching device largely depends upon respective performances of each ATM switch element which is normally constituted in the form of a one-chip device.
Also, even if an incoming ATM cell is an urgent ATM cell, e.g., an ATM cell containing information concerning human life, or the like, the ATM cell must be switched using ATM switch elements in the same manner as an ordinary (i.e., not urgent) ATM cell. Consequently, a problem occurs in that it is impossible to quickly switch an urgent ATM cell.